Which of the following is classified as a chemical heat source?

The classification of heat sources is important in understanding how they contribute to fire behavior and firefighting tactics. The heat of combustion refers to the energy released during a chemical reaction, specifically when a substance ignites and turns to combustion products. This process involves the breaking of chemical bonds and the formation of new ones, releasing substantial amounts of heat in the form of thermal energy.

This makes the heat of combustion a clear example of a chemical heat source, as it directly results from a chemical change in materials—typically when fuels like wood, gasoline, or other combustible materials undergo a combustion reaction in the presence of oxygen. Understanding this concept is crucial for fire fighters to recognize the potential dangers and how different materials will behave in a fire scenario.

The other options describe different mechanisms of heat transfer or forms of energy but do not fall under the category of chemical heat sources. Friction produces heat through mechanical means, convection involves the transfer of heat through fluid movement, and electrical resistance generates heat through the conversion of electrical energy. Each of these has its own distinct characteristics that do not relate to chemical reactions in the same way that the heat of combustion does.